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Topic: Triphenylphosphine halides (Read 65 times)

Tsathoggua

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Triphenylphosphine halides

« on: March 30, 2013, 05:39:42 AM »

Whilst browsing wikipedia, as usual, Toady ended up in hyperfocus mode and bumped into the article on triphenylphosphine dichloride. Easily synthesized from elemental Cl2 and triphenylphosphine. Dichlor, and other halogenated solvents are suitable for preparation of the compound and for reactions utilizing it.

It will chlorinate alcohols, enols and phenols into alkyl chlorides, carboxylic acids to the corresponding halide, ethers IIRC into alkyl halides. First thought was perhaps to attempt demethylation of codeine/DHC, but unfortunately it reacts with epoxides to open the ring and give either a dichloride or chlorohydrin. Damn. Ah, well..looks like it could still be of use to prepare the alkyl halides for rxn with thiourea as intermediates for the alkali metal mercaptide high-yielding route to demethylating said precursor weak opioids.

Anybody know if TPP forms dibromides/iodides in the same manner, because Br- or I- make for far better leaving groups and would presumably increase the yield of the thiolate. Not to mention be more practical to prepare when a bee doesn't have to work with noxious Cl2 gas, and the relatively low boiling points of chloroalkanes (although the BP of the haloalkane used to prepare thiolate used in the paper Toady read, 2-chloropropane is a little over 35`C, which isn't too bad, thats just a tiny bit higher than of EtOEt, which comes in with a boiling point of 34.something`C.

Anybody know if triphenylphosphine forms an analogous dibromide?

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Re: Triphenylphosphine halides

Diethoxytriphenylphosphorane (DTPP; la). Anhydrousethanol (95%, 23.4 mL, 0.38 mol) was added to sodium (9.25 g,0.40 mol), which was finely cut and suspended in anhydrous THF(60 mL) at such a rate that a moderate reflux was maintained.After the mixture was stirred overnight at ca. 25 OC, an additional20 mL of dry ethanol was added, and the resulting suspensionwas stirred for 1 h at ca. 25 OC. In a two-necked flask equippedwith a condenser, an argon inlet, and a septum, bromine (32 g,0.20 mol) was slowly added (syringe) at 0 OC (ice bath) to a solutionof TPP (52.4 g, 0.200 mol) in anhydrous diethyl ether (250 mL),under an argon atmosphere, to afford a light yellow suspensionof bromotriphenylphosphonium bromide (7) [3lP NMR (THF);6 49.7 ppml. The reaction mixture was cooled to -78 "C (dryiceacetone), and the THF' suspension of NaOEt/EtOH was addedat once under a high flow of argon gas. The reaction mixture wasvigorously stirred (ca. 30 min) while the temperature wascontrolled (dry-ice acetone bath) in order to avoid reflux, afterwhich the orange suspension turned light-brown, and becamemore soluble. Sodium bromide was decanted, and the reactionmixture was centrifuged in a 500-mL dry plastic bottle until aclear solution was obtained (2600 rpm/l5 min). The relativecomposition of DTPP (7040%) in THF was determined by 31PNMR (C6D6).